I hope you go and enjoy the retreat. You need to find out if it will be having classes, special projects to work on or just work on your own projects. I just got back from a retreat and we work on our own projects. Then one day we have a quilt picked out that all that want to join can make. It is usually an easy one day quilt. Some do it, some don't. Depends on what they have planned for the week or if they care for the pattern picked out. As for carrying your machine, just stick it in your car and don't worry about having a fancy carrier. You can get one later if you plan on doing these outings often. Save that money for fabrics.
As others have said, the other quilters are usually more than happy to assist or give advice if you ask for it. They are there for the fun of it too. No pressure.